(1) Field of the Invention
The present invention relates to an improved vehicle wheel construction, particularly bicycle wheels, including an improved connection means for connecting the spokes to the hub.
(2) Description of the Related Art
Heretofore, the vast majority of wheels have been constructed using steel wire spokes that each constitute a single structural span, with their inner end connected to the hub and their outer end connected to the rim. The spokes are generally formed from steel wire and the hub and rim may be of aluminum or steel construction. The hub, rim and individual spokes are each formed as individual components that are then joined together with mechanical connections.
The tensile forces within the spoke create relatively high stresses at their connection points and these connection points must therefore be capable of withstanding these stresses. In the conventional spoke connection arrangement, stresses due to the spoke tension are concentrated over a relatively small region of the hub flange, namely the portion of the hub flange material that is radially outward from the spoke hole. This requires that the hub flange construction be based on expensive, higher strength materials and the use of more expensive forming processes, such as forging, rather than less costly processes, such as die-casting or injection molding. Further, these stresses require that the flange be designed with robust thickness, thus adding weight to the wheel assembly.
The spoke is engaged to the hub flange with edge-to-edge contact between the head and J-bend of the spoke and the spoke hole of the hub flange, resulting in very high contact stresses at these interfaces. It is very common for the hub flange to distort due to the high contact stresses imparted by the spokes. This distortion, along with yielding of the J-bend of the spoke itself, causes the spoke pre-tension to relax somewhat, requiring frequent adjustment to maintain the alignment of the wheel rim.
More recently, in an effort to reduce the weight of the wheel assembly, some high-end wheels have been constructed using fewer spokes, each with a correspondingly higher level of spoke pre-tension. The additional pre-tension only serves to increase the stress at the hub flange connection, further exaggerating the associated problems.
The manufacture of the hub component is an expensive process. Some hub shells are machined from aluminum billet while others are cast or forged and subsequently machined. This machining operation generally requires at least three machining setups: first the cylindrical portions of the hub are turned on lathe, second, the spoke holes in one hub flange are drilled in a rotary index operation, and third, the opposite hub flange is drilled in a separate rotary index operation as well. This multi-step machining process adds considerable expense to the manufacture of the hub shell component.
Due to fabrication methods employed in conventional hub construction, it is very difficult to machine or otherwise create the details required to insure that the geometry of the hub flange conform to the spoke surface without any clearances. Such clearances allow flexure or movement under tensile loading of the spoke. With the constant cycling stress on the spoke due to the rolling of the loaded wheel, this bending flex results in premature failure of the spoke due to fatigue. In fact, the j-bend region is a very common location of the spoke breakage on bicycle wheels. Some spoke manufacturers have attempted to compensate for this shortcoming by thickening the spoke wire in this region, but this solution results in considerable extra expense and weight.
Further, it is common practice for the builder of conventional wheels to manually bend the spokes in an attempt to induce the spoke to partially conform to the hub flange and align the spoke in its direction toward the rim. This is obviously a compromise since, particularly in the case of bicycle wheels, the rim is of relatively light construction and any inconsistency in spoke tension or spoke flexure characteristics will cause the wheel to go out of true, or worse, will cause spoke breakage. When the tensile loads are not evenly shared by all of the spokes, the spokes with greater stresses will be more prone to breakage as will the portions of the rim and hub flange associated with these spokes.
It is often an objective to construct wheels with spokes that are flattened along their length to create a more aerodynamic cross-section profile. With a conventional hub flange, this creates a problem where the extra width of the flattened cross section must pass through the round hole in the hub flange. The common assembly method, when flattened spokes are utilized, requires the slotting or notching of each individual spoke hole in the two hub flanges to allow the spoke to pass through. This additional operation adds considerable expense and weakens the hub flange as well.
Accordingly, it is an objective of the present invention to overcome the forgoing disadvantages and provide an improved vehicle wheel with an improved spoke design and an improved spoke attachment to the hub.
It is a further objective of the present invention to provide a construction as aforesaid which reduces cost and provides a wheel that is light in weight and high in strength and reliability.
Further objects and advantages of the present invention will appear hereinbelow.